Studies will be conducted to elucidate structural and compositional differences between outer segments of rod (ROS) and cone (COS) photoreceptors of the retina. COS-specific monoclonal antibodies will be used to identify COS components by ultrastructural immunocytochemistry and to prepare fractions enriched in COS, including different classes of COS. Cross-reactivity of monoclonal antibodies against goldfish ROS and COS will be tested in retinas of other species to determine shared antigenic features and to map the cone mosaic in species where cone subclasses are not easily identified morphologically. The pore size of COS intralamellar spaces will be measured in different species using biotinylated extracellular tracers and avidin D-horseradish peroxidase. The interphotoreceptor space will be characterized, including measurement of the pore size of the external limiting membrane in normal and diseased retinas. Composition of the zonulae adherentes intercellular junctions that comprise the external limiting membrane will be determined by ultrastructural immunocytochemistry. Turnover of interphotoreceptor retinoid-binding protein (IRBP) in the interphotoreceptor space during the light/dark cycle will be quantified by light and electron microscopic radio-autography and biochemical techniques. Uptake and possible recycling of biotinylated-IRBP by cells that border this space will be studied using avidin D-gold ultrastructural cytochemistry. In situ hybridization will be used to determine the sites of synthesis of four retinoid-binding proteins found in the retina-retinal pigment epithelium complex: IRBP, cellular retinaldehyde-binding protein, cellular retinoic acid-binding protein, and cellular retinol-binding protein. This study will provide new information on the functional significance of these binding proteins in normal, developing, and diseased retinas.